In 1866, Ernst Haeckel said "ontogeny recapitulates phylogeny." This is now called the theory of recapitulation in genetics. I ran across it in Matt Ridley's Genome, which is the current first floor bathroom reading. It strikes me that it might be one of those paradigms borrowed by historians from scientists (not unlike Kuhn's theory of paradigms itself).

Ontogeny is the way an embryo develops. Phylogeny is the way a species evolves. The development of embryos was observed to proceed through stages from a more primitive to a more advanced state. In the primitive state, it seems to resemble "earlier" species in its evolutionary tree. Thus, each human embryo, for example, "evolves" through the stages of human evolution as it matures.

Historians seem to do something similar, when they draw parallels between, say, pre-Columbian native Americans and prehistoric European hunter-gatherers. The similaries between "primitive" peoples in the present and the distant past are assumed to outweigh their differences. Because they seem the same to us. Macrohistorians see structures and patterns "recapitulating" themselves in short and long durations, like some infinitely-regressing
Mandelbrot set. But is this real, or an artifact of the paradigm?